Chemistry · Grades 10–12
Gas laws and consistent units
Use kelvin and specify what stays constant.
Learn the idea
Ideal gas
PV = nRT is an approximate model, especially limited at high density and near condensation.
Temperature
Gas-law absolute temperatures are in kelvin, not degrees Celsius.
Variables
Boyle’s comparison keeps n and T constant; Charles’s comparison keeps n and P constant.
Units
Choose R compatible with the pressure and volume units used.
Worked examples
At constant amount and temperature, a gas has P₁ = 100 kPa and V₁ = 3 L. If V₂ = 1.5 L, find P₂.
P₁V₁ = P₂V₂ gives 100 × 3/1.5 = 200.
200 kPa
At fixed pressure and amount, volume is 2 L at 300 K. Find volume at 450 K.
V₂ = 2 × 450/300 = 3.
3 L
Check your understanding
Which temperature scale belongs in PV = nRT?
- Any scale without adjustment.
- Celsius without conversion.
- Kelvin.
Using T(K) = T(°C) + 273.15, convert 25 °C to kelvin.
Why must pressure and volume units match the chosen R?
Answers and marking notes
Answers and marking notes
- Kelvin.
The equation requires absolute temperature.
- 298.15 K
25 + 273.15 = 298.15 K.
- R has units that connect the other quantities; mismatched units create a wrong numerical result.
Dimensional consistency is essential.
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.